1. Field of the Invention
This invention relates primarily to superconducting dynamoelectric machinery, and more specifically, this invention relates to a supporting structure for a rotating superconductive field winding.
2. Description of the Prior Art
It is known that when certain materials, referred to as superconductors, are cooled to near absolute zero they exhibit a complete loss of electrical resistance. Practical utilization of the zero resistance character of superconductive materials at cryogenic temperatures has recently been applied to dynamoelectric machinery. The development of the intrinsicly stable multi-filamentary superconductor has made it possible to build stable superconducting windings with relatively high transport current densities in large direct current fields.
The use of the superconductive direct current field winding considerably increases the field magnetomotive force generated by the windings and provides greatly increased flux densities in the active air gap of the machine. This increase in flux density obtains considerably increased power density and consequential reductions in the weight and volume of the machine. Thus higher ratings for turbine generators can be obtained without prohibitive increases in frame size.
The rotor structure of conventional superconducting generators is tubular as contrasted to the solid rotor structure of normally conducting rotors. The tubular construction provides a reduction in weight as well as providing shielding, vacuum containment, and torque coupling. It has been customary to join the drive shaft to the tubular structure by means of welding. A welded construction for the superconducting rotor assembly is undesirable. The heat of welding changes the metallurgical properties of the structure which can lead to high residual stresses, and to subsequent service failure. Desirable forging properties are achieved by the initial forging and heat treating procedures and it is not possible to repeat these in the locally affected areas where welding has been performed. Welding also results in uneven temperature gradients so that subsequent machining operations can cause distortions. Thus it would be desirable to provide a unitary supporting structure for the superconducting field winding assembly of a dynamoelectric machine in which structural welding in the rotor structural members is avoided.